1. Field of the Invention
The present invention generally relates to a communication method and apparatus for a radio local area network (LAN) system, and more particularly, to a communication method and apparatus for a radio local area network (LAN) system, in which transmission performance may be improved by macrodiversity using a plurality of radio base stations.
2. Description of the Related Art
Recently, in a radio LAN system using a millimeter-wave band (for example, 30 GHz to 60 GHz), a very broad band transmission (for example, more than 100-Mbps bit rate) is developing. In this case, taking millimeter-wave transmission performance into account, communication between a transmit unit and a receive unit needs to be a line-of-sight communication.
However, for example, in a radio LAN system used in an office, a radio transmission path between the transmit unit and the receive unit may be interrupted by person's motion or movement of people. In this case, a communication signal is also interrupted and may not be transmitted. To prevent the above-discussed interruption to the communication signal, macrodiversity is proposed.
FIG. 1 shows a configuration example of a prior-art radio LAN system using macrodiversity. In the prior-art radio LAN system using macrodiversity, inside the office, for a single terminal station connected to at least one terminal unit, a plurality of radio base stations (for example, base stations 1 to n) are provided. A signal transmitted from a wiring LAN system is transmitted to the plurality of radio base stations through a HUB (an apparatus for branching a network) in an asynchronous transfer mode (ATM). Then, from the plurality of radio base stations, the signals are simultaneously transmitted to the terminal station on different frequencies (f1 to fn).
When the terminal station receives the signals transmitted from the plurality of radio base stations, the terminal station selects an optimum one (for example, a signal having a highest level) of the received signals, and demodulates a selected signal. In this way, by providing a plurality of transmission paths between a transmit side and a receive side, influence due to the above-discussed interruption to the transmission signal may be prevented. In this case, it is noted that to provide the radio LAN system shown in FIG. 1, for all of the transmission paths, substantially the same desired C/N (a ratio of energy of a modulated carrier signal to noise energy) ratio is required.
However, the following problem occurs in the above-discussed prior-art radio LAN system.
As previously discussed, in the radio LAN system, broad band transmission having a transmission rate of more than 100 Mbps is developing. In the prior-art radio LAN system shown in FIG. 1, to realize broad band transmission or more than 100-Mbps transmission rate, it is necessary for all of the transmission paths to achieve substantially the same desired C/N ratio at a transmission rate of more than 100 Mbps. In order to satisfy the above-discussed conditions, for all of the radio base stations, excessive transmit power is required, and antenna gain of all the radio base stations and the terminal station needs to be further increased.
Further, in the prior-art radio LAN system, a number of carriers corresponding to a number of radio base stations is required. Therefore, a broad transmission frequency band is required for the number of radio base stations, and, thus, efficient use of frequencies may be degraded.